The black box is commonly known as an airborne flight recorder. Two black boxes - "Flight Data Recorder" and "Cockpit Voice Recorder" - are normally installed on the aircraft. The former is used to record aircraft flight altitude, speed, heading and other flight conditions and on-board equipment, which is used to record the cockpit crew voice and other cabin sound. Two black boxes are installed at the rear of the aircraft.

Since 1903, the United States Wright brothers flew to open the journey to conquer the sky, mankind in the sky on the road to pay too many painful price. In order to ascertain the cause of the aircraft crash and to avoid the recurrence of similar flight accidents, it is envisaged to install a device capable of recording the flight status on the aircraft. In 1956, Dr. David Warren invented the first black box for civil aircraft in Australia was born. In 1957, the United States Civil Aviation Authority issued an airborne recorder regulations, requiring all flight height more than 7,000 meters, the weight of more than 5 tons of aircraft, must be equipped with a crash protection function of the recorder.

With the progress of science and technology, the black box has been in the "evolution", the record performance, survivability can be improved. Recorder from the beginning of the foil, the late 1960s tape, the early 20th century, 90 semiconductors, the development of the latest flash memory cards, recording parameters from the initial development of five to hundreds of thousands of up to a thousand, The recording time also increases exponentially. The FDR now records 25 hours of flight data and the CVR records 2 hours of cockpit voice data. As a result of the choice of titanium alloy material instead of steel shell, black box anti-crash standard from the initial can withstand 100g (gravity acceleration unit), upgrade to 3400g (gravity acceleration unit), fire resistance from 1100 degrees C 30 minutes to present the same temperature 1 Hour, anti-static extrusion, anti-seawater immersion, corrosion-resistant liquid immersion requirements have also increased. Moreover, in order to facilitate the search, the black box is also equipped with a radio beacon, once it is off the plane, it will automatically send a frequency of 37.5 kHz radio signal, a second signal to launch their own position. In general, the battery into the water after the black box to ensure that the signal transmitted at least 30 days.

Now, a more advanced intelligent ejection type black box has been put into use, its principle is similar to the fighter pilots cockpit. When the plane accident, the black box will be automatically ejected, then it in the parachute protection under the slow decline. If the black box falls into the water, the prepared inflation valve will automatically open to float on the surface. In this way, not only the black box of security has been protected, but also to facilitate people to search and salvage.

Black box about 50 cm wide and high, respectively, about 20 cm, weighing about 20 to 30 kg. It is mainly composed of base and crash survivor unit. The base is used to support and secure the crash survivor unit and is connected to the aircraft. Crash survival unit is the core component of the black box, the internal installation of data storage card, the external layer is more than a protective package to make anti-impact extrusion, high temperature, corrosion-resistant. Black box for the eye-catching orange-red, the reason is called "black" box, a statement in the plane crash it will become charred black look, one argument because it is the pilot can not interfere with the record flight Information "mysterious cassette."

Black box as the main source of evidence of the accident investigation has been universally recognized, the world most of the reasons are through the black box to find out. In the 1990s, when a Russian transport plane crashed, it was learned from the analysis of its black box that the captain brought his young son into the cockpit and allowed him to steer the stick, which was the direct cause of the crash. June 1, 2009, Air France flight 447 crash, two years after the aircraft black box was found, the French Civil Aviation Safety Investigation Bureau by analyzing the black box data, identified as a technical failure and human factors lead to plane crash. July 6, 2013, Asiana flight 214 flight at San Francisco airport, through the black box data analysis, to determine the accident is the pilot tense can not control the speed caused.

However, the black box in the air to help solve the mystery has its limitations. One case is, because the plane crashed into the sea, despite full search, but still cannot find the black box. According to statistics, from 1970 to 2009, large civil aircraft crashed the high seas of 36 incidents, 4 did not find the aircraft wreckage, 9 did not find the black box, the causes of these accidents cannot be ascertained. Another situation is that the black box record is limited, cannot determine the cause of the aircraft accident. 1998 Swiss Air 111 flight crash, because the machine's black box recorded only 2% of the electrical data, the results cannot determine whether the accident because of short-circuit fire caused the fire. Another situation is that cannot bear the huge impact of the aircraft crash, unable to resist the high pressure after the deep sea, highly corrosive, serious damage to the black box or storage data is severely damaged, cannot be effectively interpreted. In 1999, the Korean Air McDonnell Douglas 11 crash, because of this situation led to the accident investigation without result. Data show that so far at least 14 civil aviation crash, the black box did not play its due role.

In order to overcome the above limitations of the black box, some new solutions are envisaged. For example, to further improve the black box protection standards, and enhance its anti-destructive ability, it is not afraid to fight fire blisters and strong fall of the "golden box." Another example is to enhance the number of black boxes, the current two black boxes into one, and then add a set, or on the basis of the existing installation of a black box, used to record the cockpit real-time screen. However, there is a more special idea is to record the black box data in real time to the satellite, and then back to the ground by the satellite control center backup to save, so do not worry about black box cannot be found or damaged. But the problem is that the cost is too high, on-board equipment installation fees and "Internet" operating costs, making the airline unbearable.

Search for black box is an important task after the crash, but often encounter many difficulties. If the plane crashed on land, to find a black box is basically sure, and the data will be better preserved. Internationally, there is an authoritative statistics, in the land crash of the aircraft accident, the black box data survival rate of 82%. However, if the plane crashed into the sea, then the difficulty of searching for black boxes will increase, and some cannot even be found. Black box cannot find the main reason: First, the black box itself is limited power, if in a limited period of time can not accurately determine its location, then the follow-up search work will be "dark". Second, the state of the black box after falling into the water unpredictable, if the black box "independent" to sink in the sea, relatively easy to find some, if still in the wreckage of the aircraft, then you need to break through the sea to find, the most troublesome is that it Was buried deep sea mud. Third, the sea conditions are complex, especially the deep sea, the terrain as the land, mountains, valleys, gullies, in this sea conditions search only four or five bricks with the size of the cube, is indeed a "needle in a haystack. Fourth, deep-sea exploration equipment is limited. The MH370 crashed in the waters suspected to exceed the depth of the vast majority of search and rescue equipment, is investing in underwater search "bluefin tuna" underwater autonomous aircraft is also a single operation, there is no gain.

If the black box is found, it will be sent to a specialized agency for interpretation. After the necessary cleaning, drying, with professional analysis software to extract black box data stored in the data to form a black box data analysis conclusions. This takes about a few weeks or a month or so, and if the black box is damaged or there is a problem with the recorded data, the analysis time will be longer. Finally, the accident investigation agency integrated black box data analysis conclusions and other factors to obtain the final results. This process usually takes about two years. Since the analysis of black box data involves commercial and technological secrets, the process is generally not disclosed.